debugserver: remove DB interface for debug dump

Created by: unknwon

Turns out the repos.UpdateScheduler already embeds a database.DB, and no need to pass it through as the method argument.

Test plan

Manually tested:

1. Add the following lines to your sg.config.overwrite.yaml:

commands:
  repo-updater:
    env:
      SRC_PROF_HTTP: ':6060'

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Followup of https://github.com/sourcegraph/sourcegraph/pull/37915#discussion_r911758746